Windows, doors, skylights and structural components made from materials such as aluminum, alloys thereof, steel and plastics having internal hollows are known. For example, window and door assemblies may be made from metal extrusions. Devices and methods have been proposed for altering the transfer of energy through such structural components, such as thermal breaks and various types of weather stripping. Notwithstanding, alternative methods, apparatus and manufactures for modifying energy transfer through windows, doors and other structural components having internal hollows remains desirable.